Oxy-Fired Process Heaters: A Scouting Study

Transcription

1 Oxy-Fired Process Heaters: A Scouting Study 2 nd International Oxyfuel Combustion Conference Capricorn Resort, Yeppoon, Australia September 12 th 16 th, 2011 A.S. (Jamal) Jamaluddin, Walter F. Farmayan and Shu Shu Shell Projects & Technology, Houston, Texas, USA Shell Projects & Technology ECCN EAR99 August

2 Preamble Shell has placed a high priority on reducing its carbon footprint. Apart from programs to enhance energy efficiency in its various operations, initiatives are underway to evaluate various techniques for CO2 capture and sequestration (CCS). Shell also is one of seven oil companies participating in CCP (CO2 Capture Project), and one of nineteen in BIGCCS. CCP has several oxyfiring activities in its portfolio. The work described in this presentation was undertaken as part of our in-house CCS initiatives. Desktop studies were performed to evaluate the technical feasibility of oxy-firing in process heaters, followed by an economic evaluation of applying it on a refinery-wide basis Shell Projects & Technology ECCN EAR99 August

3 Outline of the Scouting Study The scope of the scouting study was as follows: - Study the effect of replacing combustion air with a mixture O2 and CO2, and a mixture of O2 and typical re-circulated flue gas, on - adiabatic flame temperature, - flammability envelope, and - flue gas emissivity Simulate the performance of a typical process heater on conventional air-firing, as well as on simulated air firing (i.e., combustion air replaced with either a mixture of O2 and CO2 (i.e., dry recycle gas), or a mixture of O2 and hot re-circulated flue gas). Compare the critical performance parameters for both scenarios. Undertake an economic evaluation of oxy-firing on a refinery-wide application for refineries at two different geographic locations. Shell Projects & Technology ECCN EAR99 August

4 T, deg F Effect on Adiabatic Flame Temperature Adiabatic flame temperature profiles for different oxidant mix and stoichiometry Adiabatic Temperature Profiles 6000 (3590 K) 5000 (3030 K) 4000 (2480 K) 3000 (1920 K) 2000 (1370 K) 1000 (811 K) Fuel Equivalence Ratio air CO2/O2: 0/1 CO2/O2: 0.79/0.21 CO2/O2: 0.75/0.25 CO2/O2: 0.7/0.3 CO2/H2O/N2/O2: 0.233/0.467/0.05/ F pht Shell Projects & Technology ECCN EAR99 August

5 Effect on Flammability Limit Calculation of Flammability Envelope Using the Minimum Adiabatic Temperature Concept Oxyfiring Flammability Envelopes (O2 Based) Comb Tadiab = 2420F (1600K) Extrapolation O Diluent Fuel-Air Line 0.25 / 0.75 O2/Diluent Line 0.25 /.75 O2/FG Air w/fg dil, 600F Pht 0.25 /.75 O2/CO2 Air w/co2 dil, 200F Pht Standard Air, No Preheat Shell Projects & Technology ECCN EAR99 August

6 Effect on Flammability Limit (Expanded View) Expanded View of the Calculated Flammability Envelope Oxyfiring Envelopes (O2 Based) <<<Fraction O2 Tadiab. = 2420F (1600K) 0.30 Combust O2 Diluent Fraction Diluent >> Fraction Combustibles >> P= Std Air, N2 Diluent, No Pht Fuel - "Standard" Air Line 0.25 //0.75 O2/Diluent "Air" Line 0.25 /.75 02/C02 Air w/c02 dil, 200F Pht 0.25 /0.75 O2/FG Air w/fg dil, 600F Pht Shell Projects & Technology ECCN EAR99 August

7 Total Emissivity Change, % Total Emissivity Change, % Effect on Emissivity Relative Improvement in Total Emissivity of CO 2 / H 2 O mixture as a Function of Temperature and Path Length 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% % Change Relative to Std. Air: for 25/75% O2/CO2 Simulated Air 0.0% PathLength Gas Temperature, Deg. F 1.64 ft. (50 cm) 3.28 ft. (100 cm) 6.56 ft. (200 cm) 16.4 ft. (500 cm) 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% % Change Relative to Std. Air: FG BasedSimulated Air CO2/H2O/N2/O2%: 23.3/46.7/5.0/ % PathLength Gas Temperature, Deg. F 1.64 ft. (50 cm) 3.28 ft. (100 cm) 6.56 ft. (200 cm) 16.4 ft. (500 cm) Shell Projects & Technology ECCN EAR99 August

8 Description of the Shell Process Heater Simulated Vertical cylindrical heater with a 48 ft tall firebox that is 23 ft in diameter. The heater has a dedicated convection section and a topmounted stack. The process tubes are divided into four flow passes, with 16 tubes in each pass in the radiant section and 14 tubes in each pass in the convection section (arranged in 14 tube-rows). All the tubes are in process service. The lowest three, out of the total of 14, rows in the convection section have bare tubes (the rest are finned). The convection tubes are 5 in diameter, while the radiant tubes are 6 in diameter. Tube metallurgy is 347SS. The heater is equipped with eight floor-mounted burners, each with a design firing capacity of 12 MMBtu/hr. The burners are fired with refinery fuel gas. Shell Projects & Technology ECCN EAR99 August

9 Compositions of the Fuel Gas Component Mole Percent in Refinery Fuel Gas Hydrogen 27.1 Carbon Monoxide 0.8 Carbon Dioxide 0.0 Methane 46.9 Ethane 8.3 Ethylene 4.4 Propane 2.3 Propylene 2.3 Butane 1.7 Nitrogen 6.0 Oxygen 0.2 Shell Projects & Technology ECCN EAR99 August

10 Heater Simulation Software xfh simulation code from HTRI (Heat Transfer Research, Inc.) was used. xfh is a PC-based program that can be used for both vertical cylindrical and cabin-style heaters. The computer model divides the radiant section into a 10 x 5 grid, uses jet theory for mixing, flame length is an input or can be calculated based on burner type, Hottel s zone method is utilized for radiative heat transfer and HTRI methods are used for in-tube flow and heat transfer calculations. xfh is not a widely used heater design software, but it was chosen because of its ability to perform more detailed radiation calculations than the typical heater design software. Shell Projects & Technology ECCN EAR99 August

11 Results of Heater Simulations Condition or Parameter Air-Fuel Combustion 25% O 2 /75% CO 2 (Dry FGR) Hot Flue Gas Recirculation Charge rate, MLbs/hr Process inlet temperature, o F Process crossover temperature, o F Process outlet temperature, o F Firing rate, MMBtu/hr Radiant duty, MMBtu/hr Average radiant heat flux, Btu/hr-ft Maximum tube temp, o F (radiant) Maximum tube temp, o F (conv) Maximum fin temperature, o F Arch flue-gas temperature, o F Stack gas temperature, o F Excess O 2 (dry basis) 2% 2% 2% Heater efficiency, % Shell Projects & Technology ECCN EAR99 August

12 A Conceptual Sketch of an Oxy-Fired Furnace Convection Section Process Heater Stack Process Tubes Burner Flame Stack Damper (Emergency Vent) Flue Gas Recycle Blower CO2 Recycle Duct Compression & Sequestration Chiller Flue Gas Recycle Damper Water CO2 CO2 Take-Off Stream Damper Venturi Mixing Duct Air-Fuel Burner Fuel Supply O 2 Enriched CO2 Oxygen Mixing Station Oxygen Supply Shell Projects & Technology ECCN EAR99 August

13 Refinery/Heater Selection for Oxy-Firing We chose two locations for refinery-wide application: - A refinery in the US - A refinery in Europe Out of the 36 heaters and 4 boilers in our US refinery, 23 heaters were chosen as candidates, with 11 of these as target heaters. Targets were chosen by priority ranking, and production capacity of a single ASU (about 3500 tons/day). The refinery in Europe had 15 target heaters. ASU (Air Separation Unit) needed at Pernis would be slightly bigger (4300 tons/day) Heaters were not considered to be candidates if: - The area is congested - The heater is too small (<75 MMBtu/hr) - The heater is isolated from other heaters Shell Projects & Technology ECCN EAR99 August

14 Site-Wide deployment: Option 1 - On-site ASU, External & Internal Power Grid power, CO2 tax included in electricity price ASU O2 Fired Heaters /Boilers Flue gas central treating & compression CO2 for sequestra tion Shell Assets On-site power generation, CO2 footprint in utilities counted as secondary emission. ASU O2 Fired Heaters /Boilers Flue gas central treating & compression CO2 for sequestra tion Shell Assets Shell Projects & Technology ECCN EAR99 August

15 Site-Wide deployment: Option 2 Pipeline Oxygen, External & Internal Power CO2 tax is included into oxygen purchase price. Grid power, CO2 tax included in electricity price O2 pipeline O2 Fired Heaters /Boilers Flue gas central treating & compression CO2 for sequestra tion Shell Assets CO2 tax is included into oxygen purchase price. On-site power generation, CO2 footprint in utilities counted as secondary emission. O2 pipeline O2 Fired Heaters /Boilers Flue gas central treating & compression CO2 for sequestra tion Shell Assets Shell Projects & Technology ECCN EAR99 August

16 Summary of Relevant Operating Data Base Case: Air-firing Air Fired Heaters /Boilers 1775 MMBtu/hr (US) 2000 MMBtu/hr (Europe) CO2 emission 855 ktons/yr (US) 945 ktons/yr (Europe) Oxy-firing Case ASU O tpd, 43.8MW (US) 4300 tpd, 53.5MW (Europe) Fired Heaters /Boilers 1575 MMBtu/hr (US) 1830 MMBtu/hr (Europe) Flue gas central treating & compression Total power MW (US) Total power MW (Europe) CO2 for 130 bar 760 ktons/yr (US) 865 ktons/yr (Europe) Shell Projects & Technology ECCN EAR99 August

17 Summary of CO2 Abatement Potential US Refinery Electricity CO2 footprint Grid electricity CO2 footprint 0.61 ton/mwh US grid On-site power footprint 0.24 ton/mwh on-site cogen 85% 1. On-site ASU case CO2 footprint associated with power 56.4 MW Mtpa import power 56.4 MW Mtpa on-site power 2. Imported O2 case MW Mtpa import power MW Mtpa on-site power CO2 emission base case Mtpa power price($/mwh) CO2 avoided, on site ASU and imported power Mtpa CO2 avoided, on-site ASU and on-site power Mtpa 50 CO2 avoided, imported O2 and power Mtpa CO2 avoided, imported O2 and on-site power Mtpa 50 European Refinery Electricity CO2 footprint Grid electricity CO2 footprint 0.45 ton/mwh US grid On-site power footprint 0.24 ton/mwh on-site cogen 85% 1. On-site ASU case CO2 footprint associated with power 67.9 MW Mtpa import power 67.9 MW Mtpa on-site power 2. Imported O2 case MW Mtpa import power MW Mtpa on-site power CO2 emission base case Mtpa power price($/mwh) CO2 avoided, on site ASU and imported power Mtpa 98 CO2 avoided, on-site ASU and on-site power Mtpa 50 CO2 avoided, imported O2 and power Mtpa 98 CO2 avoided, imported O2 and on-site power Mtpa 50 Shell Projects & Technology ECCN EAR99 August

18 CO2 Abatement Cost from GCAT Shell Projects & Technology ECCN EAR99 August

19 Technology Plan for Oxy-Firing Pilot Test A pilot test with the following objectives would be the logical next step: Verify that the concept of utilizing the existing burners for oxy-firing can be safely applied. Compare heater performance with air-firing. Quantify the CO2 concentration and NOx reduction achievable. The pilot test will involve the following activities: Tests performed in a single-burner test furnace. An appropriate O2 injection system, a duct, plenum, etc., will need to be installed. Start up will be on air-firing, with gradual switch over to O2+RFG. The pilot test should be followed up with a multi-burner demonstration phase test prior to full-scale deployment. Note: The test-plan mentioned above is being pursued through CCP s focus area on oxy-fired process heaters. Shell Projects & Technology ECCN EAR99 August

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